boldsoftware Use this skill whenever the user wants something drawn or diagrammed (architecture, flow, sequence, mind map, sketch — anything visual). It renders an Excalidraw canvas inside the chat (view-only — user can pan/zoom but not edit; iteration happens by you editing the JSON) with Download .excalidraw, Download PNG, Copy SVG, Copy PNG, and Copy JSON buttons.
Workflow
- Write the renderer page to
/tmp/excalidraw.html(template below). - Write the diagram to
/tmp/diagram.jsonas a JSON array of elements (skeleton format — see below). - Call
output_iframewithpath=/tmp/excalidraw.html,files={"elements.json": "/tmp/diagram.json"}, andlibraries=["excalidraw"]. - On user feedback ("move the DB right", "add a cache layer") edit the JSON and call
output_iframeagain. - If the user clicks Copy JSON in the canvas and pastes scene JSON back, parse it and use it as the new source of truth.
The canvas is view-only because the sandbox blocks edits-out: any change the user made would be silently lost on the next render. Iteration happens by you editing the JSON, or by the user copy/pasting JSON or SVG (with embedded scene) back.
The libraries parameter is essential: it tells the host page to stream the excalidraw runtime into the iframe out-of-band, so the (~2.5 MB) bundle does not get stored in the conversation. Without it, window.__LIBS__ will never resolve.
Renderer template (excalidraw.html)
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<style>
html,body { margin:0; padding:0; height:100vh; font-family:sans-serif; }
#toolbar { display:flex; gap:8px; padding:6px 10px; background:#f5f5f5; border-bottom:1px solid #ddd; align-items:center; font-size:13px; }
#toolbar button { font:inherit; padding:4px 10px; cursor:pointer; }
#status { color:#888; margin-left:6px; }
#editor { width:100%; height:calc(100vh - 40px); }
#err { color:#b00; white-space:pre-wrap; padding:8px; font:12px monospace; }
</style>
</head>
<body>
<div id="toolbar">
<button id="download">Download .excalidraw</button>
<button id="download-png">Download PNG</button>
<button id="copy-svg">Copy SVG</button>
<button id="copy-png">Copy PNG</button>
<button id="copy-json">Copy JSON</button>
<span id="status"></span>
</div>
<div id="editor"></div>
<div id="err"></div>
<script type="module">
try {
const { render } = (await window.__LIBS__).excalidraw;
const raw = window.__FILES__["elements.json"] || "[]";
render({ elements: typeof raw === "string" ? JSON.parse(raw) : raw });
} catch (e) {
document.getElementById("err").textContent = "Excalidraw error: " + (e.stack || e.message);
}
</script>
</body>
</html>
The template is intentionally minimal — toolbar markup plus one render() call. The button ids (download, download-png, copy-svg, copy-png, copy-json) and the editor mount id (editor) are wired up by the excalidraw library. Don't rename them. Any button you omit from the toolbar HTML is simply not bound — e.g. drop copy-png if you don't want it.
Copy SVG embeds the full scene JSON in the SVG (via exportEmbedScene), so pasting that SVG into excalidraw.com restores the diagram exactly. (This skill only ingests the JSON elements array, not SVG — if a user pastes SVG back, extract the embedded <!-- payload-start -->... JSON and use that as the new elements source.)
Element format
Elements go through convertToExcalidrawElements, which accepts a "skeleton" form simpler than raw Excalidraw JSON. Required per element: type, x, y, width, height. Give each element a unique id if anything references it (we pass regenerateIds: false so ids survive).
Sensible defaults are applied: strokeColor="#1e1e1e", backgroundColor="transparent", fillStyle="solid", strokeWidth=2, roughness=1, opacity=100. Canvas is white.
Shapes
- Rectangle / Ellipse / Diamond:
{ "type": "rectangle", "id": "r1", "x": 100, "y": 100, "width": 200, "height": 80 }."roundness": { "type": 3 }for rounded corners."backgroundColor": "#a5d8ff", "fillStyle": "solid"for filled.- Add a label with
"label": { "text": "Hello", "fontSize": 20 }— auto-centered, no separate text element needed. Works on rectangle, ellipse, diamond, arrow.
- Standalone text:
{ "type": "text", "x": 150, "y": 138, "text": "Title", "fontSize": 24 }.xis the left edge. To center atcx: width ≈text.length * fontSize * 0.5, sox = cx - text.length * fontSize * 0.25. - Arrow / Line:
{ "type": "arrow", "id": "a1", "x": 300, "y": 150, "width": 200, "height": 0, "points": [[0,0],[200,0]], "endArrowhead": "arrow" }.pointsare[dx,dy]offsets fromx,y.endArrowhead∈null | "arrow" | "bar" | "dot" | "triangle". Use"line"for an unarrowed connector.
Arrow bindings (preferred shorthand)
Attach an arrow to shapes by referencing their ids. convertToExcalidrawElements synthesizes the full bindings (focus, gap) and updates the shapes' boundElements:
{ "type": "arrow", "id": "a1", "x": 100, "y": 50, "width": 200, "height": 0,
"points": [[0,0],[200,0]], "endArrowhead": "arrow",
"start": { "id": "r1" }, "end": { "id": "r2" } }
Referenced ids must exist or the binding is silently dropped and the arrow floats.
Color palette
Primary strokes: #4a9eed blue, #f59e0b amber, #22c55e green, #ef4444 red, #8b5cf6 purple, #ec4899 pink, #06b6d4 cyan, #84cc16 lime.
Pastel fills (use with fillStyle: "solid"): #a5d8ff (input/source), #b2f2bb (success/output), #ffd8a8 (warning/external), #d0bfff (processing), #ffc9c9 (error), #fff3bf (notes/decisions), #c3fae8 (storage), #eebefa (analytics).
Background zones (use opacity: 30): #dbe4ff UI layer, #e5dbff logic layer, #d3f9d8 data layer.
Sizing
Diagrams display at ~700px wide. Design the bounding box to be roughly 4:3 so the canvas isn't squished.
- Common scene extents: 400×300 (close-up), 600×450 (section), 800×600 (default), 1200×900 (overview — keep fonts ≥18pt).
- Font minimums: 16 body/labels, 20 titles, 14 annotations only. Below 14 is unreadable at display scale.
- Element minimums: 120×60 for labeled boxes. Leave ≥20–30 px gaps.
- Array order is z-order: earlier elements draw first (behind). Background zones → shapes → arrows → top-level text / decorative icons.
Worked example
Two connected labeled boxes:
[
{ "type": "rectangle", "id": "b1", "x": 100, "y": 100, "width": 200, "height": 100,
"roundness": { "type": 3 }, "backgroundColor": "#a5d8ff", "fillStyle": "solid",
"label": { "text": "Start", "fontSize": 20 } },
{ "type": "rectangle", "id": "b2", "x": 450, "y": 100, "width": 200, "height": 100,
"roundness": { "type": 3 }, "backgroundColor": "#b2f2bb", "fillStyle": "solid",
"label": { "text": "End", "fontSize": 20 } },
{ "type": "arrow", "id": "a1", "x": 300, "y": 150, "width": 150, "height": 0,
"points": [[0,0],[150,0]], "endArrowhead": "arrow",
"start": { "id": "b1" }, "end": { "id": "b2" } }
]
Common pitfalls
- Overlapping elements: check coordinates so labels, boxes, and zones don't stack.
- Title centering:
xis the left edge. Use the formula above; don't trusttextAlignfor positioning (it only affects multi-line wrap). - Long arrow labels overflow short arrows — shorten the label or widen the arrow.
- Aspect ratio: a very tall or very wide bounding box squishes into the iframe. Rearrange or pad to roughly 4:3.
- Broken bindings: arrow
start/endids must match an existing shape'sid.